1. Field of the Disclosure
This application relates to a lubricating structure for a hybrid vehicle configured to transmit power, which is output from an engine or a motor or both, to a drive shaft is a planetary gear mechanism.
2. Description of Related Art
International Application Publication No. 2013/094043 describes an invention that relates to a hybrid vehicle. In the hybrid vehicle that uses a first motor, a second motor and an engine as driving force sources, the hybrid vehicle includes a planetary gear mechanism and a brake mechanism. The planetary gear mechanism transmits power, which is output from the first motor or the engine or both, to a wheel side. The brake mechanism stops the rotation of one rotating element (specifically, a rotating element to which an output shaft of the engine is coupled) of the planetary gear mechanism. The invention described in the international Application Publication No. 2013/094043 is intended to suppress a decrease in the durability of the above-described planetary gear mechanism. For this purpose, the controller described in the International Application Publication No. 2013/094043 is configured to, in a state where the rotation speed of each of pinion gears of the planetary gear mechanism increases, reduce as driving torque shared by the first motor within a required driving torque as the rotation speed of each pinion gear increases.
The International Application Publication No. 2013/094043 describes the configuration of a powertrain including a single-pinion-type planetary gear mechanism as an example of a vehicle that is a controlled target. The single-pinion-type planetary gear mechanism includes a sun gear, a ring gear and a carrier. The first motor is coupled to the sun gear. The second motor and the drive shaft are coupled to the ring gear via a gear train. The engine is coupled to the carrier via the brake mechanism. With such a configuration, by outputting torque from both the first motor and the second motor in a state where the rotation of the engine and the rotation of the carrier are stopped and locked by the brake mechanism, it is possible to efficiently cause the vehicle to perform motor running at high power. That is, as indicated by the dashed line in the nomograph of FIG. 3 in the international Application Publication No. 2013/094043, during motor running using the two motors as described above, the rotary shaft of the carrier and the rotary shaft of the engine are locked by engaging the brake mechanism, and the rotation speed of the carrier and the rotation speed of the engine are fixed to zero. By driving the first motor in a rotation direction opposite to the rotation direction of the second motor that is driven during ordinary motor running in this state, it is possible to perform motor running at high power.
When motor running is performed by using the two motors while the rotation of the carrier is locked as described above, the pinion gears of the planetary gear mechanism rotate at a high speed. That is, as shown in FIG. 3 in the International Application Publication No. 2013/094043, the sun gear coupled to the first motor and the ring gear coupled to the second motor rotate in mutually opposite directions, so the rotation speed of each pinion gear increases as the rotation speeds of those first motor and second motor increase. Because the first motor outputs torque, a load that is exerted on the pinion gears also increases. Therefore, the temperature of the pinion gears rises, which leads to a state where seizure or abrasion easily occurs. Against such an inconvenience, in the controller described in the International Application Publication No. 2013/094043, the output of the first motor is more limited as the rotation speed of each pinion gear increases, and an increase in the rotation speed of each pinion gear is suppressed, as described above. Therefore, an excessive increase in the rotation speed of each pinion gear is avoided, so it is possible to suppress a decrease in the durability of the planetary gear mechanism due to seizure or abrasion of the pinion gears.
Even in a state where an increase in the rotation speed of each pinion gear is suppressed by limiting the output of the first motor as described above, it is required to supply oil to the pinion gears for lubrication and cooling. However, in the International Application Publication No. 2013/094043, the amount, state, or the like, of oil that is supplied to the planetary gear mechanism is not sufficiently taken into consideration. When the rotation of the carrier and the rotation of the engine are locked by the brake mechanism as described above, an oil pump that is driven by the engine stops. Therefore, supply of oil to the planetary gear mechanism and the like, in that case is generally limited to splash lubrication by the use of gears. In splash lubrication by the use of gears, it is possible to lubricate and cool the surfaces of the above-described pinion gears; however, there is a case where lubrication and cooling performance may not be sufficient for the inside of each pinion gear and a pinion shaft supporting each pinion gear.
The amount and state of oil that is supplied through the above-described splash lubrication change depending on an oil temperature and a vehicle speed. For example, as shown in FIG. 9, when the vehicle speed is low, the rotation speed of each of gears that splash oil is low, so the amount of oil supplied reduces as compared to when the vehicle speed is intermediate or high. When the viscosity of oil is high because of a low oil temperature as well, the amount of oil supplied reduces. When the viscosity of oil is low because of a high oil temperature or when the rotation speed of each pinion gear is high because of a high vehicle speed, oil supplied to the pinion gears does not adhere to the pinion gears and is rejected because of centrifugal force, with the result that the amount of oil that is supplied to the pinion gears decreases.
In this way, when the planetary gear mechanism that transmits power in a state where the rotation of the carrier is locked as in the case of the hybrid vehicle described in the International Application Publication No. 2013/094043 is used, there is still room for improvement in order to appropriately supply oil to the pinion nears the planetary gear mechanism for the purpose of lubrication and cooling of the pinion gears.